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News4's Darcy Spencer reports on a vigil held for two little children killed in Germantown. Police charged their mother and another woman with the murder. (Published Saturday, Jan 18, 2014)

Updated at 2:07 PM PST on Monday, Jan 20, 2014

A second woman has been arrested in the stabbing deaths of two toddlers in Germantown, Md., in what investigators say was an attempted exorcism.

Monifa Denise Sanford, 21, was arrested Saturday afternoon after she was released from the hospital. Sanford was injured during the violent incident Friday morning, in which the toddlers were killed and two other children were hurt.

Investigators said that the children's mother -- Zakieya Latrice Avery, 28, of Germantown -- and Sanford, who lived with the family, believed they were performing an exorcism.

"Cases like this are heartbreaking," said Montgomery County Police Chief Tom Manger. "Our thoughts are with the family and friends of the victims along with the 911 operators, police officers, evidence technicians, and fire and EMS personnel that responded."

Authorities were alerted to the scene Friday after a neighbor called 911, saying she saw a car with its door open and a knife on the sidewalk outside the house. Police who responded said the car's keys were still in the ignition, and there was blood in the car.

Police believe the red-handled knife they found on the sidewalk may be one of the weapons used in the attack.

Officers had to force their way inside the house, where they found the children inside in a "very bloody" crime scene. They were found in the bedrooms and may have been asleep at the time of the attack.

Police were called to the home Thursday, the evening before the brutal attack.

A neighbor told a 911 operator he had seen a baby inside a car parked outside the home for approximately 45 minutes. During the phone call, the neighbor says he was approached by two women, one of whom said she left the baby inside the car because there was something going on inside the home and she didn't want her child to be endangered.

The caller told the operator the women then "chased him down" while one of them talked to herself.

Neighbors organized a vigil to remember the little boy, Norell, and the little girl, Zyana.

"How can you hurt a child?" said one attendee. "To me, to hurt a child, you are a coward."